Communications networks such as the Internet allow users to retrieve network resources, such as web pages provided by web servers connected to the network, using computing devices connected to the network. In some cases, the web servers may collect and store information about the user or the computing device used to retrieve the network resource. This information may include demographic information explicitly provided by the user (e.g., user's age, sex, etc.) and information about the computing device (e.g., operating system, manufacturer, etc.).